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PY-EXCE0002 · bounded_exception_region

Keep each try, except, else, and finally clause narrowly scoped.

This is a deterministic rule for python. Read its implementation.

Definition

Section titled “Definition”

Count the executable statements inside every try, except, else, and finally clause, including the statements nested below a compound if, loop, context manager, or match case, and return the largest count any one clause reaches. A nested function, a nested class, and a nested try each open their own scope and are counted there instead.

A wide protected region is what makes an exception handler ambiguous. Four statements under one try means four things could have raised, so the handler below it is answering for a failure nobody can name, and the recovery it performs is right for at most one of them.

Evidence

Section titled “Evidence”

The finding names the clause, its line, and its statement count. The value is the largest clause statement count in this file. How specific the caught type is stays a separate question, owned by Ruff BLE001 and Pylint W0718.

Exceptions

Section titled “Exceptions”

A file with no exception clause at all measures zero. The count is a measurement and a project policy owns the ceiling, so a resource protocol that has to acquire and use in one protected region raises it rather than fighting it. The repository’s Git ignore files or a per-rule glob can exclude generated or vendored sources. Widening the ceiling is only right when moving a statement out would change the protected transaction or the cleanup guarantee.

Examples

Section titled “Examples”

A try clause holding only payload = path.read_text() beneath an except OSError measures 1, and the failure boundary is unambiguous. A try clause that reads a file, parses it, transforms the model, and updates shared state measures 4, and its handler now answers for four different failures. A handler clause holding a log call and a re-raise measures 2.

References

Section titled “References”